I like Guinness quite a bit, but I didn't like it when I was younger. A lot of dark beers are heavy or have a bitter taste, so you may want to just give one a shot sometime to see if it meets your tastes.
Most people like the Bud Lights of the world because despite the counter-culture, it's light, has a fairly innofensive taste, and is easy to drink. If you like that and you're in the right region of the U.S., Id suggest giving Yuengling a try. I've only seen it in the east coast, though, couldn't find it when I lived in Illinois.
If you want more lighter beers, I'd suggest looking into Leinenkugel beers, usually pretty light and have various brews that are very flavorful, some almost don't taste like beer if you don't typically like the taste of beer.
I'd personally avoid something like Heineken. They often taste a little "skunky", for a lack of a better word. I've been told it's partially because they ship in Green bottles, and if they sit in the sun/heat too long, it'll penetrate the glass & affect the flavor of the beer, although I don't know if that's 100% true.
Beer is something where you'll realistically have to give a few a shot and learn. Your tastes may change over time as well.